SICAMG

Car has been running perfect and it did something very strange today.
Outside temp was 48* and thats the coldest it has been since I did some inter cooler work,more boost,15 psi "normal reading", and new tune. Got on it hard and wound it up good to see what the IAT was going to be after the inter cooler work and car lost power all of a sudden. AFR showed 19.1 Was at 10.5 then instantly shot to 19.1...melt down AFR for sure !!! and lost power of course. Tried it again real quick and same thing. So this is what I do know. IAT was at it's lowest 80* so my work payed off.Fuel pressure was at 75 and holding and the gauge did register vacuum in the parking lot at work so thinking MAP sensor is good, but....could it be possible the boost hit the limp mode threshold ? That's the only thing I was not watching and I do not know what limp mode would do in an over boost condition.
Long story short now I can not duplicate the problem and it's back to normal but it is also 80* again outside.
This is a sure fire way to blow an engine and glad I have a real time wide band in it. Any ideas ??

BoostedAero

***Sorry in advance for text wall***

Gary, sorry to hear about this... that is scarier than when I was running on 1 pump due to the adapter cable NOT being used by the dealer during warranty recall of tank/pumps/sender

When I was running w/o adapter cable I would jump into 11.9/12.2 around 3500-3800 then it would just climb into the low 13.1/13.3 range toward 5500 plus and I would have to just let off so I didn't wet myself with fear

I took it back to them they added the cable now I am running rich and just need a retune

On your car, I would think for sure you had a voltage hiccup/fuel supply hiccup. How many miles/years are on the pumps? How does the relay socket look?

Is there a chance you may have sucked something in through the pump pickup and the injector(s) got semi-clogged with debris and then it blew it out?

I would probably run techron/seafoam through your car (2x 8 gallon tanks back to back.)

Inspect wiring loom at fuel relay and pin-out on fuel hat for over voltage signs. You may have a pump taking a crap or high resistance which would need investigating further.

Honestly, temp differential can cause havoc on electrical signal transmission on aging oxidized connections

BBirdwell had a good write up on fuel relay maintenance with some conductive paste:

https://mbworld.org/forums/w211-amg/...intenance.html

It seems worth cleaning all connections and applying the paste for assurance of seamless voltage transmission on these cars with their age.

I just dealt with another issue that was hard to diagnose as no failure showed up in STAR. A dying but not dead wiper motor that was causing a voltage drop while running that would drop the car into 11.1v then back up to 13.9v...causing symptoms similar in feeling to the mechanical bull I rode a few times after too many drinks at a few bars in college :-/ Unplug the wiper motor symptom disappeared

I learned how intricate, intertwined and fragile the electrical systems are on these cars.

Post an update on what you are finding... I am certainly curious

SICAMG

Will...it couldn't be fuel pressure because it was holding at 75 psi and that's normal for me to see. This was almost an instant 19 AFR and I felt it like a "bump" sort of which was an instant drop in power.
I will pop in another MAP sensor and keep an eye on the boost. Maybe tomorrow since it will be cold in the morning I will throw ice in the cooler tank to really exaggerate things and see what does. I have raced it in this configuration all year but.. its never been this cold. I would be hard pressed to see more than 16lbs of boost and that would be 1 lb over normal. I will keep you posted!

Huey52

Thanks very much for the detailed and photo'd insight!!

C32owner

Not your map sensor. You hit the map limit of 17psi in an overboost situation and the car goes into some sort of limp mode switching to a fueling map, albeit a freaking dangerous fuel map under boost as because like you witnessed the AFR goes time bomb lean.. Only way to clear is to shut off the car and restart, that resets the fuel map it was on.. Well this is what I experienced as well. Your cold temperatures would have raised your boost just enough to hit the limit I rate

SICAMG

All set with a map clamp installed. Can see 17lb's with no problem now.

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This is a sure fire way to blow an engine and glad I have a real time wide band in it. Any ideas ??[/QUOTE
Another reminder for those that runs modified cars without wideband,can save the engine!!

SICAMG

What has saved my engine many times is the fail safe set up. Worth it's weight in gold !!

C32owner

Well then I am stumped.

SICAMG

What do you mean buddy ? The Map sensor is giving a voltage higher than the ECU is calibrated for so lets say 4.0volts triggers the limp mode. Set the clamp at 3.75 and now the ECU only see's that voltage as it's maximum..
Are you thinking of something else ??

C32owner

No what I meant was, I was convinced your issue was from the sensor hitting the map limit and causing your dangerous condition, but as you said you have a map clamp on protecting you from the limit being reached, that now I am stumped as in I don't know what is causing your issue. Have you data logged on a cold night run, to make sure you don't some how hit the map limit even with the clamp set?

SICAMG

No that was the problem all along and now with the clamp it is all set !! No more limp mode.
My bad for not reading your reply a little better. My clamp was set to high and was pushing into the limp mode zone so had to set it much lower to get around the issue.

C32owner

Ah got you, awesome news you sorted now. Enjoy the power

C32owner

Finally ordered my map clamp to resolve my lean map issue as well. Any tips or pictures you got to share of where you spliced the wiring harness to install this and what settings you used on the map clamp? As a matter of interest, not that the ecu sees less voltage from the map sensor xwhen you data log and see the boost, is your boost pressure lower on your logs as the ecu sees a lower signal value? Obviously however the motor still sees full boost

SICAMG

Boost is capped do to you setting that threshold limit. so when looking at logs it stays pegged at max boost. I did have to also set it lower than expected and did a lot of testing with different voltages to see if the AFR would be effected and it was not.

C32owner

Thanks that was my next question was, if your afr went lean with the ecu seeing less boost but motor running full boost. Glad to see afr stayed the same.

Did you just literally cut the map. Sensor wires and put the map clamp inline?

SICAMG

Yes. I extended the wires over to the driver side shock tower and velcroed the box to the body so this way I could make quick easy adjustments. Make sure you use the correct size wire and solder all connections.

C32owner

Thank you! Off hand do you know the correct size wire or is that in the map clamp instructions booklet?

SICAMG

Just run good, flexable same size wire and you will be fine.

C32owner

Cheers bro